PARENT SESSION
PW11 - Site-Specific Risk Assessments
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P857) A Screening Level Risk Assessment of Historical Copper Levels in San Francisco Bay.
Arnold, W*,1, Lee, C2, 1 Copper Development Association Inc., New York, NY2 International Copper Association, New York, NY
ABSTRACT- Studies were conducted in San Francico Bay to determine the ability of the Biotic Ligand Model to predict toxicity in estuarine waters. Results indicated that dissolved organic carbon (DOC) concentrations explained much of the variability in toxicity. Though factors in addition to DOC mitigate the potential for copper toxicity, a first attempt to characterize risks in San Francisco Bay was made by adjusting potential exposure using DOC alone. DOC and measured dissolved copper Mytilus edulis EC50's were regressed. Mytilus edulis is the most sensitive organism in EPA's saltwater quality criteria database and is the basis for the present saltwater quality criteria. A simple model was developed using the slope of the regression and adjusting the y-intercept to 7.6 ug/L (the Geometric mean of EC50s for the Granite Canyon reference station). Doing so resulted in an equation that describes a conservative lower bound estimation of EC50s based on DOC. Using historical San Francisco Bay Regional Monitoring Program DOC data from 1993-1999, EC50s were estimated for each station and date using the simple model. Each resulting EC50 was subsequently divided by the EPA acute to chronic ratio of 3.127 to estimate a potential no effect concentration (PNEC). Subsequently, the dissolved copper concentration measured for each location and date was divided by its respective PNEC. Thus, if the ratio of the measured dissolved copper to PNEC is >1 it would indicate that a potential risk for negative effects existed at the location and date. All PEC/PNEC ratios suggest that no unacceptable risk existed at any station on any date for which data was collected.
Key words: copper, risk, estuarine, San Francisco Bay